As a part of the development and design of an integrated circuit (IC) chip, prototype chips are made in small volumes and tested. In one type of test, inputs are supplied to the chip and the outputs are then compared to what the chip is supposed to provide. This allows specific parts of the chip to be checked, tested and debugged before volume production begins. When problem areas are found, these parts of the chip are exposed to more rigorous testing. One type of rigorous testing is to aim an optical probe at a problem area and observe the problem area while the chip is being operated. Optical probes can also be helpful when the production process changes or to improve quality or yield during production.
It is important during such observations to operate the chip at all of the temperatures for which it is designed. A chip that might run properly by design at room temperature might fail when it is particularly cold or hot. This type of testing may be particularly important for chips in mobile devices that often lack fans, heaters, and stable room temperatures. Such devices often have extended temperature requirements. Some products may require reliable operation at temperatures ranging from −40 to +110 C. The optical probe must therefore be able to operate through this temperature range.
In addition, optical silicon debug is trending towards more sightings at cold temperatures including, less than 10 C and even sub-zero junction temperatures. There is a need for probing low power devices. Some such devices have such low power that they that cannot self-heat. Hot junction temperatures above the current 60 C optical probe operating temperature range are also being tested.
Current optical probes use a liquid immersion lens (LIL) in conjunction with a diamond window to get beyond a 10 C-60 C temperature range. The LIL limits productivity and capability because it does not have enough resolution to image small features on the chip. As technology moves from 32 nm to 22 nm process technology and beyond, a LIL becomes unable to resolve many of the important features and solid immersion lenses (SIL) are being considered.